The invention relates to a method and apparatus for electrolytic treatment of liquids, especially waste waters, being presented in the preamble portions of the independent claims.

In Finnish Patent Application 890493 and International Patent Application PCT/FI87/00101 is disclosed a process where liquid to be treated is passed between two plate-like electrodes having opposite charges, and medium is introduced into the reaction area separately from the liquid to be treated, for example through holes made by perforating the electrode plate. The method has proved advantageous in the practice in the sense that the medium which is introduced between the plates and can contain substances participating in an electrolytic reaction, on one hand can contribute to creating turbulence within the reaction area when desired, thus helping to prevent the passive layers in the vicinity of the plates and to keep the surfaces of the plates clean, and on the other hand it allows to dose the substance participating in the reaction more uniformly to the reaction area, because in this way too high initial concentration of the substance participating in the reaction can be avoided in the beginning of the reaction area, which otherwise would be the case if the medium were fed together with the liquid to be treated into the reaction area between the electrodes.

It has been now found out that the method and apparatus can be improved, if the supply of the liquid to be treated and the medium are arranged to take place in a certain manner with regard to each other. In accor¬ dance with this finding the method and apparatus of

the invention are mainly characterized by what is disclosed in the characterizing portions of the inde¬ pendent claims.

By providing a pulsating feed of at least one of the material flows, for example to take place in cycles, the special features of the inventions can be utilized in an optimal manner.. The pulsating volumetric flow rate taking place by virtue of the feed in the through flow channel between the electrodes allows the electro¬ lytic reaction to proceed in phases in such a manner that when the flow is stopped in the reaction area, the necessary electrolytic reactions can take place, and when the flow advances forward, the necessary mixing occurs. Further, as the liquid is a suspension or emulsion from which one of the phases will be precipitated in the process, it can be assumed that the alternately decelerated and accelerated flow taking place as early as in the reaction phase improves the separation of the substances.

The invention will be described in the following more closely with reference to the accompanying drawing, wherein

Fig. 1 shows an apparatus used in the method in a view showing the principle, and

Fig. 2 shows the reaction chamber comprising the reaction area in a sectional view, the section being taken along the direction of the flow.

Fig. 1 shows schematically an apparatus in which the method according to the invention can be used. The apparatus comprises a reaction chamber 1 comprising a through flow channel to which the liquid to be treated is f d along a pipe 2 by means of a pump 3. The

reaction chamber is also supplied with a medium separately from the liquid supplied through the pipe 2, the medium being supplied through a pipe 4 by means of a pump 5. The treated liquid is passed from the through flow channel along a pipe 6.

In accordance with the invention the flows emerging from the pipes 2 and 4 to the through flow channel are so arranged that a pulsating flow will be present in the channel, that is, the flow taking place forward between the electrode plates is alternately accelerated and decelerated. In the practice this can be ac¬ complished by allowing either of the pumps 3 and 5 to effect a pulsating flow, in which case a hose pump (so-called peristaltic pump) or an air pump can be used as the pump for example. Because the volumetric flow of the medium supplied through the pipe 4 is smaller than that of the liquid to be treated, it is preferred that the pump 5 of the medium serves as the pump causing the pulsating flow, and a centrifugal pump suitable for handling large volumetric amounts and causing a flow of constant volumetric flow rate can serve as the pump for the supply of the liquid to be treated.

The flow fed through the pipe 4 is preferably a substance participating in the electrolytic reaction, for example solution containing chloride, such as sodium chloride solution. The method can be used in all conventional waste water treatment methods utili¬ zing substances in ionic or gaseous state generated in the electrolysis. Some of the examples of such methods are precipitation of heavy metals, preci¬ pitation of oil emulsions as well as oxidation of dissolved impurities, such as cyanide. Further, the method can be used also in the treatment of other substances as well, for example in the bleaching of pu.. suspension, the oxidating chlorine needed in the

bleaching being generated within the through flow channel with the help of the chloride supplied as the mediu .

Fig. 2 shows the construction of the reaction chamber 1 in more detail. Inside the reaction chamber there is n through flow channel 8 which is formed between two plate-like electrodes 7 of opposite charges and in which also the reactions caused by the electro- lysis take place and which serves as passage for the flow of the liquid to be treated. The plates 7 of a rectangular shape form therebetween an elongate flow channel in the direction of their larger dimensions, said channel being limited in the direction of the planes of the plates by the outer walls of the reaction chamber, which can be of an electrically insulating material. In the case of Fig. 2 the reaction chamber is disposed vertically, the channel being situated in an upright position, that is, the main flow channel leads upwards. The liquid to be treated is supplied through the pipe 2 to the lower end of the channel, from where it flows along the channel 8 to its upper end, from where it is removed through the pipe 6. By this provision the elongate vertical plates are better covered with the liquid, and the gaseous products of electrolysis gather to the space in the upper end of the chamber wherefrom they can be easily removed. The treated liquid is passed through the pipe 6 to a possible aftertreatment, for example to a precipitation basin. In some processes the flotation effect by the electrolytically generated gas distributed in small bubbles in the liquid is utilized, in which case the precipitation basin can have also a drag for collecting the material on the surface of the basin. Further, any heavy precipitate possibly accumulated in the chamber can easily be removed from the lower end of the chamber.

The medium is fed through the pipe 4 to the other side of the electrode plates, for example into sta¬ bilizing or intermediate containers 9, from where it enters the channel 8 by means of holes 7a going through the electrode plates 7. The holes are formed in the plate-like electrode material by drilling and the size and distribution can be adapted to the need. Only one of the plates can be provided with such holes. The electrodes can be formed of any suitable electrode material, depending on the process. These kind of materials are for example stainless steel, nickel- plated steel, platinum-plated titanium, consumable anodes iron and aluminum that are in common use in flocculation processes etc.

The pump 3 and pump 5 can be synchronized with regard to each other also in the fashion that the "pushing stage" will be alternately in the pump 5 feeding the medium and in the pump 3 feeding the liquid to be treated. The pulsating flow within the channel 8 can also be achieved by the arrangement where only one of the pumps causes the pulsating volumetric flow. The above-mentioned synchronizing of the pumps in respect of each other brings about the advantage that in every instant when the volumetric flow of one of the pumps is at its minimum it will not cause flow resis¬ tance to the maximum flow of the other pump. Despite of the synchronizing the flow forward in the flow channel 8 will retain its pulsating character, because the total volumetric flow caused by the pump 3 is greater than that caused by the pump 5.

The distance between the plates can lie in the range of 1 to 10 cm and the plates can have the width of ca. 15 cm. The height, that is, length of the flow channel can be 60 to 260 cm. It is also possible to provide the flow channel with several plates one after the other. The apparatus can also be assembled starting from several chambers 1, in which case they can be cou led for exam le in series.